1. Field of the Invention
The present invention relates to photoconductive members sensitive to electromagnetic waves including infrared rays, visible rays, ultraviolet rays, X-rays, .gamma.-rays, etc.
2. Description of the Prior Art
Photoconductive materials constituting photoconductive layers in solid-state image pickup devices and in image-forming devices, e.g. electrophotographic image forming members and original-reading devices, are required to have characteristics such as high sensitivity, high S/N ratio [photocurrent (Ip)/dark current (Id)], absorption spectral properties fitting the spectrum of the electromagnetic waves to be used for irradiation, quick light responsiveness, desired dark resistivity, and harmlessness to human body during service, and further in solid-state pickup devices, easiness of afterimage treatment. Particularly the harmlessness to human body during service is important to the photoconductive materials to be incorporated into electrophotographic appliances for office purposes.
A photoconductive material recently noticed on the basis of the above points is amorphous silicon (hereinafter designated as a-Si), which is described, for example, in German Pat. Offen. Nos. 2,746,967 and 2,855,718 as an electrophotographic image forming member and in German Pat. Offen No. 2,933,411 about application thereof to photoelectric reading devices.
However, prior art photoconductive members having a photoconductive layer formed of a-Si still need overall improvement in characteristics including electrical, optical, and photoconductive properties such as dark resistivity, photosensitivity, and photo-responsiveness, environment resistances such as humidity resistance, and long-term stability of performance characteristics.
For instance, under the prior art a-Si type of photoconductive member is used for electrophotographic image forming members, attempts to enhance the photosensity and dark resistance at the same time often bring about undesirable effects such that; residual potential is observed frequently during service; fatigue accumulates in repeated continuous operations for long hours and thereby leads to the appearance of a so-call ghost phenomenon that is the occurrence of a residual image; and the responsiveness gradually deteriorates in high-speed repeated operations.
In addition, a-Si has relatively low absorption coefficient for light waves longer than shortside visible light waves. Accordingly, the prior art photoconductive layer made of a-Si is ineffective in utilizing either the energy of a semiconductor layer which is in practical use today or the longer-wave energy of a halogen lamp or fluorescent lamp, when these light sources are used for the irradiation of the photoconductive layer. This is one of the still remaining problems to be solved.
Meanwhile, when a large portion of illuminating light arrives at the substrate (support) of a photoconductive member without being absorbed by the photoconductive layer, light interference due to multiple reflection will occur in the photoconductive layer if the substrate has a high reflectance for the light incident thereupon through the photoconductive layer. This interference is a cause of the "unfocused image".
As the irradiation spot is made smaller for the purpose of improving the resolution, the above effect becomes greater, and particularly when a semiconductor laser is employed as light source, this effect is a serious problem.
Moreover, when the photoconductive layer is made of a-Si, hydrogen atoms or halogen atoms such as fluorine or chlorine atoms are incorporated thereinto for the purpose of improving electrical and photoconductive properties thereof and boron atoms, phosphorous atoms, or some other atoms are also incorporated for the purpose of controlling the type of the electric conduction, where a problem arises occasionally in the electrical or photoconductive properties of the resulting layer depending upon the manner of the incorporation. For instance, the problem is that photocarriers produced in the resulting photoconductive layer by light irradiation are insufficient in lifetime or that the injection of charge from the substrate side in the dark area is not sufficiently impeded.
Furthermore, in the formation of the photoconductive layer thicker than ten and several m.mu., a phenomenon such as the rising or peeling of the layer from the substrate or cracking in the layer is liable to develop with the time of leaving the product in the air after withdrawal thereof from the vapor deposition chamber used for the layer formation. This phenomenon is remarkable in particular when the substrate is of a drum type which is commonly used in the field of electrophotography. Thus the photoconductive layer involves the problem of long-term stability.
Accordingly, it is necessary to improve characteristics of a-Si itself and, on the other hand, to solve all the problems stated above in the design of the photoconductive member.